Gallium nitride (GaN) based power devices have been regarded as promising candidates for high-frequency and high-power applications owing to the superior material properties such as high polarization-induced 2DEG density, high electron saturation velocity and high critical breakdown electric field. By using GaN instead of silicon, system efficiency can be boosted and also a smaller system volume can be achieved. Despite these advantages, self-heating has been a major hindrance to the deployment of AlGaN/GaN HEMTs in RF/microwave and power electronics applications. The small area occupied by this class of semiconductor chips results in a need to dissipate the heat uniformly and efficiently.
GaN based high electron mobility transistors (HEMTs) are naturally depletion mode (D-mode) devices, which means that when there is no control signal on the gate terminal, the conducting channel is normally on. The on-state resistance of GaN power devices strongly depends on geometry of the layout design.
To deal with this problem, a low voltage silicon MOSFET is usually series-connected with a D-mode HEMT to create a hybrid E-mode device. A prior approach using multiple dies and devices included a series connection of an E-mode HEMT with a D-mode HEMT and a series connection of a silicon MOSFET with a GaN HEMT. However, in such multiple device or multiple die configurations, heat dissipation efficiency was unfavorable.
In addition, prior layout topologies lacked scalability and uniformity on the bare die level when flip-chip packaged on a PCB with good heat dissipation capability such as metal or ceramic based PCB.